Field of the Invention
The present invention relates to an imaging apparatus and a camera system. More particularly, the present invention relates to an imaging apparatus that can be used for camera systems such as digital still cameras and digital video cameras.
Description of the Related Art
Japanese Patent No. 4,027,113 Publication (to be referred to as “Patent Literature 1” hereinafter) proposes a solid state image sensor (imaging apparatus) that can be used for digital still cameras and digital video cameras and in which ranging pixels having a ranging feature are arranged as part or all of the pixels of the image sensor for detection by means of a phase difference method.
Each ranging pixel has a plurality of photoelectric conversion sections and is so configured that luminous fluxes that pass through different pupil areas of the camera lens are guided to different photoelectric conversion sections.
Then, optical images (to be referred to as ranging images hereinafter) formed by luminous fluxes that have passed through different pupil areas are acquired by means of the signals obtained by the photoelectric conversion sections contained in each ranging pixel.
The distance to an object can be measured by computing the amounts of defocuses by means of triangulation using stereo images on the basis of the amounts of discrepancies of the ranging images.
Thus, any distance can be measured highly accurately at a high speed by means of this arrangement because, unlike the conventional contrast method, the camera lens does not need to be moved to measure the distance.
Additionally, the signals obtained by the plurality of photoelectric conversion sections contained in each ranging pixel can be used for the pixel value of the ranging pixel for producing a picked-up image.
When an image of a low luminance object is picked up by means of an imaging apparatus having such ranging pixels, only a small quantity of light enters each photoelectric conversion section of a ranging pixel. Then, as a result, the intensity of the acquired signals becomes low so as to degrade the S/N ratio and the quality of the signals.
When, on the other hand, an image of a high luminance object is picked up, a large quantity of light enters each photoelectric conversion section. When the quantity of light that enters a photoelectric conversion section exceeds a predetermined threshold value, the amount of electric charge that is subjected to photoelectric conversion and accumulated exceeds a tolerance value. Then, the obtained signal is saturated at a maximum value and the signal can no longer be acquired accurately. For this reason, an image sensor having such known ranging pixels cannot acquire high quality signals when detecting the distance to a low luminance or high luminance object and picking up an image thereof.
Then, in a ranging operation of measuring the distance to an object, both the accuracy of ranging images and the ranging accuracy fall.
Additionally, in an operation of producing an image, both the accuracy of the pixel values of ranging pixels and the quality of a picked up image fall.